1. Field of the Invention
The present invention relates to a fuel cell separator and a method for manufacturing the same.
2. Background Art
As typical examples of fuel cells, polymer electrolyte fuel cells are known. FIG. 7 is a cross-sectional view illustrating an example of such a fuel cell, in which a membrane electrode assembly 3 having an electrolyte membrane 1 and a pair of electrode layers 2 each of which has a sequential stack of a catalyst layer 21 and a diffusion layer 22 and is formed on each side of the electrolyte membrane 1 is provided, and the opposite sides of the membrane electrode assembly 3 are sandwiched between separators 5,5 each having gas flow channels 4, whereby a single fuel cell unit is formed. An electrolyte membrane 1a protrudes beyond the periphery of the electrode layers 2, and a space between the protruding electrolyte membrane 1a and the separators 5 is filled with a gasket 6 as an adhesive having a sealing function in such a manner that all of the members are integrated, whereby sealing between the two electrode layers 2,2 is ensured. Though not shown, a resin frame may be disposed between the gasket 6 and the separator 5 in some cases. In such a case, an adhesive is further applied between the resin frame and the separator so that they are integrated.
In order for a fuel cell unit to exhibit excellent power generation performance over a long period of time, the durability of the seal between the gasket and the separator or between the resin frame and the separator can be an important factor. However, since product water that will be produced by a power generation reaction contains acids, fluorine ions, and the like, such product water containing acids, fluorine ions, and the like could cause the bonding interface between the gasket 6 and the separator 5 or the bonding interface between the resin frame and the separator to deteriorate, thus failing to ensure seal durability. In an extreme case, the separator could become corroded due to the influence of the product water.
In order to avoid the aforementioned problem, Reference 1 (JP Patent Publication (Kokai) No. 2007-12300 A) discloses a fuel cell separator in which an anticorrosion resin coating layer is formed on part of the surface of the separator (a region corresponding to a non-power generating region of the surface of the separator). With such a resin coating layer formed, the anticorrosive effect of the separator can be increased. In addition, when a seal member such as an adhesive or a gasket is disposed on the separator with the resin coating layer interposed therebetween, seal durability would also be ensured. The resin coating layer is formed by, for example, electrodepositing a cationic resin, which has been obtained by ionizing resin powder such as epoxy resin, urethane resin, acrylic resin, or polyimide resin, on the surface of the separator.
As another example of a fuel cell separator that solves the same technical problem, Reference 2 (JP Patent Publication (Kokai) No. 2007-242576 A) discloses a fuel cell separator and a method for manufacturing the same, in which cathodic electrolysis in an alkaline solution is applied to a surface of a peripheral portion of a separator made of stainless steel, excluding gas flow channels (a conducting section), so that a hydrated iron oxide film is formed on the surface of the peripheral portion of the separator, and further, a resin sheet layer made of an aqueous electrodeposition resin is electrodeposited on the hydrated iron oxide film. Examples of such aqueous electrodeposition resins include amine resins.
Hydrophilic aqueous resins are environmentally friendly materials and are often used as materials of resin coating layers. However, since a separator made of stainless steel has a surface on which a passive film made of a chromium oxide layer is formed, the separator has low affinity for hydrophilic aqueous resins. Thus, when a resin sheet layer made of an aqueous electrodeposition resin is directly formed on the surface of the separator made of stainless steel, the resin would have low adhesion to the separator and thus could easily peel off the separator. Thus, when a hydrated iron oxide film is formed at the interface between the surface of the separator made of stainless steel and the resin coating layer as described in Reference 2, adhesion between the separator and the resin coating layer increases, whereby a fuel cell separator with high corrosion resistance and increased durability can be provided.